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Ghrelin Induces Abdominal Obesity Via GHS-R-Dependent Lipid Retention

Jeffrey S. Davies, Pia Kotokorpi, Sinan R. Eccles, Sarah K. Barnes, Pawe F. Tokarczuk, Sophie K. Allen, Hilary S. Whitworth, Irina A. Guschina, Bronwen A. J. Evans, Agneta Mode, Jeffrey M. Zigman and Timothy Wells

School of Biosciences (J.S.D., S.R.E., S.K.B., P.F.T., S.K.A., H.S.W., I.A.G., T.W.), Cardiff University, Cardiff, Wales CF10 3AX, United Kingdom; Department of Biosciences and Nutrition (P.K., A.M.), Karolinska Institutet, Novum, S-14157 Huddinge, Sweden; Department of Child Health (B.A.J.E.), School of Medicine, Cardiff University, Cardiff, Wales CF14 4XN, United Kingdom; and Departments of Internal Medicine and Psychiatry (J.M.Z.), University of Texas Southwestern Medical Center at Dallas, MC9077, Dallas, Texas 75390-9077

Address all correspondence and requests for reprints to: Dr. Timothy Wells, School of Biosciences, Cardiff University, Cardiff CF10 3AX, Wales, United Kingdom. E-mail: wellst{at}cardiff.ac.uk.

Circulating ghrelin elevates abdominal adiposity by a mechanism independent of its central orexigenic activity. In this study we tested the hypothesis that peripheral ghrelin induces a depot-specific increase in white adipose tissue (WAT) mass in vivo by GH secretagogue receptor (GHS-R_1a)-mediated lipolysis. Chronic iv infusion of acylated ghrelin increased retroperitoneal and inguinal WAT volume in rats without elevating superficial sc fat, food intake, or circulating lipids and glucose. Increased retroperitoneal WAT mass resulted from adipocyte enlargement probably due to reduced lipid export (ATP-binding cassette transporter G1 mRNA expression and circulating free fatty acids were halved by ghrelin infusion). In contrast, ghrelin treatment did not up-regulate biomarkers of adipogenesis (peroxisome proliferator-activated receptor-2 or CCAAT/enhancer binding protein-) or substrate uptake (glucose transporter 4, lipoprotein lipase, or CD36) and although ghrelin elevated sterol-regulatory element-binding protein 1c expression, WAT-specific mediators of lipogenesis (liver X receptor- and fatty acid synthase) were unchanged. Adiposity was unaffected by infusion of unacylated ghrelin, and the effects of acylated ghrelin were abolished by transcriptional blockade of GHS-R_1a, but GHS-R_1a mRNA expression was similar in responsive and unresponsive WAT. Microarray analysis suggested that depot-specific sensitivity to ghrelin may arise from differential fine tuning of signal transduction and/or lipid-handling mechanisms. Acylated ghrelin also induced hepatic steatosis, increasing lipid droplet number and triacylglycerol content by a GHS-R_1a-dependent mechanism. Our data imply that, during periods of energy insufficiency, exposure to acylated ghrelin may limit energy utilization in specific WAT depots by GHS-R_1a-dependent lipid retention.

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